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Abstract: Electrochemical measurements on pincer ligands bis‐N‐(2,5‐dimethoxyphenyl)pyridine‐2,6‐dicarbothioamide (pdcta) and 6‐(4,7‐dimethoxy‐2‐benzothiazolyl)‐N‐(2,5‐dimethoxyphenyl)‐2‐pyridinecarbothioamide (pbcta) in N,N‐dimethylformamide (DMF) and dimethylsulfoxide (DMSO) on a glassy carbon working electrode revealed sulfur centred electrochemical processes. Spectroscopic, elemental and electrochemical analyses indicated that pdcta coordinated to Pd(II) via a κ3‐SNS mode to give 1 whereas pbcta coordinated via a κ3‐SNN mode to give 2. Electrochemical measurements in DMF indicated that the reduction of Pd(II)→Pd(0) proceeded in a concerted manner in the 2, whereas reduction was resolved into the Pd(II)→Pd(I)→Pd(0) in the case of 1. In the presence of p‐toluenesulfonic acid, both palladium complexes displayed electro‐catalytic proton reduction in DMF, with associated overpotentials calculated to be 97 mV and 156 mV for 1 and 2, respectively. The data suggests that the κ3‐SNS pincer ligand enhances the activity of the Pd(II) towards proton reduction relative to 1. [ABSTRACT FROM AUTHOR]

• Two Co(II)-pincer ligands of coorcination modes κ3-SNS and κ3-ONS are reported. • The crystal structure of the pincer ligand pcta is reported. • Both complexes of Co(II) displayed electro-catalytic hydrogen evolution (HER). • The addition of co-ligands bpy or PPh 3 had varying effects on the HER. Bis- N -(2,5-dimethoxyphenyl)pyridine-2,6-dicarbothioamide (pdcta) and N -(2,5- dimethoxyphenyl)-6-[(2,5-dimethoxyphenyl)carbamothioyl]pyridine-2-carboxamide (pcta) were synthesized from a one pot mixture as pincer ligands. Crystals of pcta , grown from CDCl 3 were structurally characterized, and found to crystallize in the space group P 2 1 / c. The Co(II) complexes [Co(II)(κ3-SNS-pdcta)(CH 3 CO 2)(H 2 O)] (1) and [Co(II)(κ3-ONS-pcta)(CH 3 CO 2)(H 2 O)]·H 2 O (2) were prepared from the reaction of pdcta and pcta and Co(CH 3 CO 2) 2 ·4H 2 O in ethanol at reflux under argon atmosphere. The identities of 1 and 2 were confirmed from their elemental analyses, ESI MS and a series of spectroscopic measurements. Both complexes displayed electrocatalytic hydrogen evolution with p -toluene sulfonic acid monohydrate in the presence and absence of bpy or PPh 3 co-ligands. The hydrogen evolution occurred at moderate overpotentials (605–780) mV, with 1 giving better Faradaic efficiencies than 2 under all the conditions explored herein. Thermodynamic estimates, based on the reduction potentials, suggest that the homolytic pathway for the production of hydrogen from the CoIII-hydride species generated in the presence of the proton source, is more favourable than the heterolytic pathway in CH 3 CN. [ABSTRACT FROM AUTHOR]

The synthesis and crystal structures of bis-N-(2,5-dimethoxyphenyl)pyridine-2,6-dicarbothioamide (dicarbothioamide I) and 6-(4,7-dimethoxy-2-benzothiazolyl)-N-(2,5-dimethoxyphenyl)-2-pyridinecarbothioamide (L1) as well as the syntheses of the palladium(II) chloride and acetate pincer complexes are reported. The stability constant for the palladium complex formation at 25°C was found to be (2.04 ± 0.26) × 104 dm3 mol-1 and (2.30 ± 0.19) × 104 dm3 mol-1 with ΔfH = 8 ± 1 kJ mol-1, ΔfSθ = 108 ± 10 J K-1 mol-1, and ΔfH = 17 ± 4 kJmol-1 and ΔfSθ = 140 ± 20 JK-1mol-1 for the PdClL1 and Pd(OAc)L1, respectively. The kinetics of formation of the palladium(II) complexes were investigated and the mechanism is proposed to be associative in nature (ΔH‡1 = 34 ± 2 kJ mol-1 and AS‡1 = -113 ± 8JK-1 mol-1, and ΔH‡1 = 37 ± 3 kJ mol-1 and ΔS‡1 = -100 ± 8 JK-1mol-1 for the PdClL1 and Pd(OAc)L1 species, respectively). The electrochemical measurements of the acetonitrile solutions revealed irreversible electron transfers consistent with the electrochemical decomposition of the ligand and its coordination complexes. [ABSTRACT FROM AUTHOR]

Abstract: Potential of zero charge and interfacial capacitance values of ω-mercaptoalkanoic acid monolayers deposited on Au(111) are derived from immersion current transients, and are applied to the analysis of their acid properties. Potential of zero charge and capacitance titration curves extend over six pH units, and exhibit apparent pK1/2 values that vary with electrolyte concentration. Electrostatic adsorption of protons at the monolayer-solution boundary provides a quantitative explanation of these observations, and leads to a diffuse layer corrected pK a value of 4.3, which is independent of the thiol chain-length. [Copyright &y& Elsevier]